Question: Which of these numbers is composite? ${41,\ 43,\ 61,\ 83,\ 87}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 41, 43, 61, and 83 each have only two factors. The factors of 87 are 1, 3, 29, and 87. Thus, 87 is the composite number.